Environmental control system incipient failure indicator apparatus

ABSTRACT

An incipient failure indication apparatus for an environmental control system which includes a heat exchanger through which air flows and a temperature control thermostat. The indication apparatus includes an indicator having an alarm in communication with a control board, the control board in communication with the thermostat. The alarm has a visual indicator and/or an aural indicator, whereby the attention of a person is attracted to the indicator upon activation of the alarm. A first temperature sensor is disposed on the upstream side of the heat exchanger and a second temperature sensor is disposed on the downstream side of the heat exchanger, whereby the temperature sensors respectively sense the temperature of the air upstream and downstream of the heat exchanger. The first and second temperature sensors are in communication with the control board, and the control board has means for comparing the temperatures sensed thereby. The control board also includes means for activating the alarm in response to recognizing a difference in temperatures sensed by the first and second temperature sensors which is one of greater than and less than a predetermined value. The apparatus may also be provided with a timer, a reset switch in communication therewith, a filter service time indicator, and means for activating the filter service time indicator a predetermined period measured by the timer after the reset switch is activated. The apparatus may also be provided with means for activating a remote alarm upon activation of the alarm, whereby persons outside of a building serviced by the environmental control system are notified of an incipient failure of the environmental control system.

BACKGROUND OF THE INVENTION

The present invention relates to building heating and cooling systems,particularly as used in a residence, and performance monitoringapparatuses therefor.

Rather than suddenly and completely fail, the environmental controlsystem which controls the temperature of the interior of a building mayexperience a performance degradation which may not be immediatelysensibly noticed by the occupants of the building, and which may occurduring a period over which the performance of the system is continuallydegrading, eventually leading to a complete failure. Often, buildingoccupants notice the degradation in performance only when they sensethat their environment is uncomfortably hot or cold, by which time theenvironmental control system may have completely failed. At this point,the occupants are left with an inoperable environmental control system,and must contact an appropriate repair facility to investigate theproblem and make the appropriate repairs. Also, once the occupantsnotice that the system is not operating properly, they are left to theirown devices to contact an appropriate repair facility to undertakerepairs. Therefore, a considerable period of time may pass before therepair personnel are contacted and arrive to address the failure, duringwhich time the occupants may be completely without heat or airconditioning.

In some cases, the gradual degradation of system performance, which maygo unnoticed by the occupants, may be indicative of a problem which willeventually result in a sudden system failure or other types of concerns.For example, in some cases, if the refrigerant charge level of an airconditioning system drops to a level which is too low to adequatelycarry oil back to the compressor for lubrication of some interfacingsurfaces therein, excessive wear or seizure of the compressor mayresult.

Further, many environmental control systems utilize a filter forcleaning the air which is heated or cooled by the environmental controlunit. These filters require cleaning or replacement, usually by theoccupants, after a period of use. A dirty filter restricts airflowthrough the unit, which inhibits the system's ability to force airthrough the ductwork and interchange the air in the building. Often,replacement of the filter is neglected by the user, and the performanceof the system consequentially degrades.

A way to identify environmental control system performance degradationbefore complete system failure occurs is thus highly desirable. Further,a way of automatically contacting the appropriate repair facility, sothat personnel at the facility will become aware and initiate repair ofthe failing system is also desirable. Additionally, a reminder by whichthe occupants will be notified that the filter should be replaced or atleast inspected, the filter having completed its anticipated normal useperiod, is also highly desirable.

SUMMARY OF THE INVENTION

The present invention addresses each of the above issues by providingnotice to the occupants and, in certain embodiments, an appropriaterepair facility as well, of a degradation in environmental controlsystem performance.

The present invention provides an incipient failure indication apparatusfor an environmental control system which includes a heat exchangerthrough which air flows and a temperature control thermostat. Theindication apparatus includes an indicator or annunciator having analarm in communication with a control board, the control board incommunication with the thermostat. The alarm has a visual indicatorand/or an aural indicator, whereby the attention of a person isattracted to the indicator upon activation of the alarm. A firsttemperature sensor is disposed on the upstream side of the heatexchanger and a second temperature sensor is disposed on the downstreamside of the heat exchanger, whereby the temperature sensors respectivelysense the temperature of the air upstream and downstream of the heatexchanger. The first and second temperature sensors are in communicationwith the control board, and the control board has means for comparingthe temperatures sensed thereby. The control board also includes meansfor activating the alarm in response to recognizing a difference intemperatures sensed by the first and second temperature sensors which isone of greater than and less than a predetermined value.

An embodiment of the present invention may also provide a timer and areset switch in communication therewith, a filter service timeindicator, and means for activating the filter service time indicator apredetermined period measured by the timer after the reset switch isactivated.

Further, an embodiment of the present invention may also provide meansfor activating a remote alarm upon activation of the alarm, wherebypersons outside of a building serviced by the environmental controlsystem are notified of an incipient failure of the environmental controlsystem.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of the presentinvention, and the manner of attaining them, will become more apparentand the invention will be better understood by reference to thefollowing description of embodiments of the invention taken inconjunction with the accompanying drawings, wherein:

FIG. 1 is a front view of a thermostat and an incipient failureapparatus indicator unit mounted in a common housing, the housingmounted to an interior wall of a building;

FIG. 2 is a second embodiment of an incipient failure apparatusindicator unit having an individual housing;

FIG. 3 is schematic of a heat pump-type of environmental control unit,to which the inventive incipient failure indicator apparatus is adapted;

FIG. 4 is a flow chart illustrating the logical control of oneembodiment of the inventive incipient failure indicator apparatus to theenvironmental control unit of FIG. 3;

FIG. 5 is a schematic of a first combination furnace and airconditioner-type environmental control unit, to which the inventiveincipient failure indicator apparatus is adapted; and

FIG. 6 is a schematic of a second combination furnace and airconditioner-type environmental control unit, to which an alternativeembodiment of the inventive incipient failure indicator apparatus isadapted.

Corresponding reference characters indicate corresponding partsthroughout the several views. Although the drawings representembodiments of the present invention, the drawings are not necessarilyto scale and certain features may be exaggerated in order to betterillustrate and explain the present invention. The exemplifications setout herein illustrate embodiments of the invention, and suchexemplifications are not to be construed as being exhaustive or to limitthe scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, there is shown attached to interior wall 20 of abuilding combination thermostat and incipient failure indicator unit 22.Thermostat 24 and indicator unit or annunciator 26 are enclosed incommon housing 28 which gives the combination a unified appearance.Thermostat 24 is of an electrical type well-known in the art, andincludes controls 30 and display 32 and may regulate both heating andcooling operations. Thermostat 24 may be provided with manually actuated3-position heat/off/cool selector switch 33, or may automatically choosewhich of heating and cooling operations is to be performed.

Indicator unit 26, according to one embodiment of the present inventionincludes a flashing lamp or light emitting diode (LED) 34, and speaker36 through which a buzzer or other aural notice may be issued. LED 34and speaker 36 are activated upon recognition of an incipientenvironmental control system failure as disclosed herein below.Indicator unit 26 also comprises on/off switch 38 by which the speaker36 may be disabled without interfering with the operation of flashingLED 34, the illuminated LED continuing to remind the user that anincipient failure of the environmental control system has been detected.

Indicator unit-26 further includes lamp or LED 40 which indicates to theuser that the filter of the environmental control unit should becleaned, replaced or at least inspected, the predetermined period oftime over which it has been in service having elapsed. Indicator unit 26includes push button reset switch 42 which resets the timer whichmeasures the period of time over which air flows through the filter.Notably, LEDs 34 and 40 are of different colors (e.g., in one embodimentLED 34 is red and LED 40 yellow) thereby quickly indicating to theoccupant the nature of the warning issued by the indicating unit. Also,while it is envisioned that LED 34 will flash, LED 40 will remainsteadily illuminated. Further, although not shown, each of the switchesand LEDs of indicator unit 26 are appropriately labeled to apprise theoccupant of the type of the warning being issued by the indicator unit.

Referring now to FIG. 2, there is shown a second embodiment of anindicator unit according to the present invention, here indicator unit26 is not housed in a common housing with the thermostat, as shown inFIG. 1, but rather is provided with a separate housing 44. Indicatorunit 26, housed in housing 44, is attached to an interior wall of thebuilding adjacent to an existing thermostat such as thermostat 24 whichis also provided with a separate housing (not shown), facilitating readyadaptation of the inventive incipient failure indicator unit to apreviously-installed environmental control system. Alternatively, inapplications where the environmental control unit is located in a closetreadily accessible to the occupant, housing 44 for indicator unit 26 maybe attached directly to the airhandler or furnace housing thereof. If soinstalled, the aural alarm issued by the indicator unit may be easilyheard by the occupant to attract the occupant's attention to the closetand the indicator unit. As described above, housing 44 is provided withappropriate labels associated with each of the switches and LEDs ofindicator 26 to immediately apprise the occupant of the type of warningbeing issued thereby.

Referring now to FIG. 3, there is shown a first embodiment of anenvironmental control unit to which the inventive incipient failureindicator apparatus is adapted. Environmental control unit 46 is of theheat pump variety and is contained within housing 48. Environmentalcontrol unit 46 includes blower 50 for drawing interior air into housing48, and forcing the air through refrigerant-to-air heat exchanger 52. Asshown, heat exchanger 52 is an “A” coil-type heat exchanger which, as iswell known in the art, serves as a refrigerant system evaporator duringcooling or air conditioning operation, and as a refrigerant systemcondenser during heating or “furnace” operation, the refrigerant systemto which A coil 52 is connected not shown. Heat pumps are well-known inthe art, and thus a discussion of their refrigerant system componentryand operation is not provided herein.

Air heated or cooled by A coil 52 is then directed to ductwork 54, whichconveys the heated or cooled air throughout the building. As is typicalwith heat pump units, environmental control unit 46 is provided withauxiliary heater 56 within housing 48, downstream of A coil 52. Thepurpose of auxiliary heater 56 is to provide supplemental heat in heatmode. Auxiliary heater 56 is of a known type which may be electrical orhydronic.

Filter 58 is provided to clean the air flowing through housing 48 beforeit reaches the blower or the heat exchanger. Arrows 60 shown in FIG. 3indicate the flow of air sequentially through filter 58, A coil 52,blower 50, auxiliary heater 56, and out of housing 48 through ductwork54.

With the inventive incipient failure apparatus indicator adapted toenvironmental control unit 46, temperature sensor elements 62 and 64 areplaced within housing 48, in the airflow respectively upstream anddownstream of A coil 52. Temperature sensor elements 62 and 64 are, inthe exemplary embodiment, thermistors (special semiconductor diodeswhose conductivity increases with the diode temperature). Alternatively,with appropriate modifications to the control means, sensors 62 and 64may be thermocouples. So arranged, thermistor 62 senses the temperatureof the air flowing through housing 48 before it is heated or cooled by Acoil 52, and thermistor 64 senses the temperature of the air flowingthrough housing 48 after it has been heated or cooled by A coil 52. Notethat although thermistor 64 is shown located upstream of auxiliaryheater 56, it may alternatively be located downstream thereof. As willbe discussed further below, when auxiliary heater operation has beendetected, the incipient failure warning apparatus of the presentinvention becomes inoperational until the need for auxiliary heating haspassed and the operation of auxiliary heater 56 has been terminated bythe heat pump system control (not shown) which determines whetherauxiliary heating is called for and activates auxiliary heater 56.

Referring now to FIG. 4, there is shown one embodiment of the logicassociated with the inventive incipient failure indication apparatus.The control board for the logic shown in FIG. 4 is in electricalcommunication with thermostat 24 and, through thermistors 62, 64, withthe interior of environmental control unit 46. In certain embodiments ofthe present invention, the control board of the incipient failureindication apparatus (not shown) may be comprised of a daughter boarddirectly fitted and electrically connected to a separate mother board(not shown) located on environmental control unit 46 and which controlsaspects of environmental control beyond the scope of the presentinvention. The mother board provides the daughter board with inputs suchas, for example, power, an auxiliary heater signal or a blower signal.The daughter board may be designed to be readily fitted onto the motherboard, providing easy adaptation of the inventive incipient failureindicator system to certain existing environmental control units,whereby the incipient failure indicator system may be readily adapted toa wide variety of environmental control units, or exclusively adapted toa particular model or brand of environmental control unit.Alternatively, a single control board may be used for control of theenvironmental control system and incipient failure indication inaccordance with the present invention.

The input to the control board of indicator unit 26 includes, referringto the top row of FIG. 4, signals received from thermistors 62 and 64,which are respectively designated T1 and T2. As will be describedfurther hereinbelow, the difference in temperatures sensed bythermistors 62 and 64 is compared to a predetermined value fordetermining whether the performance of the environmental control systemhas degraded, indicating an incipient system failure. Note that thethermostat signal is abbreviated “TS” in the flowchart.

Another input to indicator unit 26 is the signal from the thermostat,which indicates whether it is calling for heating or cooling, or if theenvironmental control system has been turned off (in which case nothermostat signal is received by indicator unit 26). Some environmentalcontrol systems may not include air conditioning, and the thermostatsignal issued thereby to indicator unit 26 would be only an “on” signal.The logic shown in FIG. 4 and described below would be easily modifiedto accommodate such a system.

As seen in FIG. 4, low voltage power is also provided to indicator unit26, and the source thereof may be shared between thermostat 24 and theindicator unit. If the environmental control unit to which the inventiveincipient failure indicator apparatus is adapted is a heat pump, asshown in FIG. 3, an auxiliary heater signal will be received byindicator unit 26. The auxiliary heater signal, abbreviated “A.H.” inthe flowchart, is a digital indication of whether the heat pumpcontroller (not shown, but which may be the above-mentioned motherboard) is calling for supplemental heat during heating operation.Finally, a blower signal input is provided to indicator unit 26. Theblower signal indicates when blower 50 (FIG. 3) is operating, and thusdrawing air through filter 58.

The control board of the incipient failure indication apparatus firstdetermines whether a thermostat or an auxiliary heating signal is beingreceived. If not, the logic branches to the left as shown in FIG. 4 andback up to the input of flow chart symbol 66, and remains in this loopuntil a thermostat signal is received and auxiliary heating signal isreceived. Once this condition exists, the indicator apparatus will waitfor a period of time before continuing its finction, thus allowing astabilization period for the environmental control system to reach itssteady state operating condition. As shown in symbol 68 of the flowchart of FIG. 4, this waiting period is seven minutes, although it maybe slightly shorter and may certainly be longer. Once the seven minutewait has been completed, the logic proceeds downward from symbol 68 tosymbol 72.

In symbol 72, the logic of the indicator apparatus control board againdetermines whether a call for auxiliary heating is being detected. Ifso, the logic loops back to the input to symbol 66 and remains in thisloop, and the apparatus remains on hold, until the auxiliary heatingsignal has ceased. The above-mentioned seven minute wait is performed(symbol 68) before proceeding again to symbol 72. If an auxiliaryheating call is not detected, the logic of the indicator unit controlboard then determines whether cooling or heating is called for accordingto the thermostat signal received. If cooling is called for, the logicproceeds downward from symbol 70 to make a comparison of thetemperatures sensed by thermistors 62 (T₁) and 64 (T₂). Symbol 74indicates that if the sensed temperature difference across A coil 62 isgreater than the lower predetermined value of 12° F., and less than thehigher predetermined value of 30° F., the environmental control systemis assumed to be operating properly, and no incipient failure isanticipated. The logic thus loops back to the input of symbol 72 andcontinues.

Although symbol 74 indicates that the lower predetermined value to whichthe difference between T₁ and T₂ is compared is 12° F., it is envisionedthat a slightly smaller lower predetermined value, for example 10° F.,may provide adequate detection performance, but will lessen thesensitivity of the indicator apparatus. It is also envisioned that aslightly larger lower predetermined value, for example, 15° F., may alsoprovide adequate detection performance, but may render the indicatorapparatus overly sensitive and result in false alarms. Further, althoughsymbol 74 indicates that the higher predetermined value to which thedifference between T₁ and T₂ is compared is 30° F., it is envisionedthat a slightly larger higher predetermined value, for example 32° F.,may provide adequate detection performance, but will lessen thesensitivity of the indicator apparatus. It is also envisioned that aslightly smaller higher predetermined value, for example, 28° F., mayalso provide adequate detection performance, but may render theindicator apparatus overly sensitive and result in false alarms. Thoseskilled in the art will understand that actuation of the alarm in theevent of the difference between T₁ and T₂ being equal to or greater thanthe higher predetermined value (e.g., 30° F.) may be indicative ofdegraded airflow performance, perhaps caused by an excessively dirtyfilter. It is envisioned, however, that substantially satisfactoryperformance may be obtained by an embodiment in which the sensedtemperature difference between sensors 62 and 64 is compared duringcooling operation (symbol 74) to only a lower predetermined value (e.g.,12° F.), rather to both lower and higher predetermined values asdescribed above. Those skilled in the art will also appreciate thatthere are a variety of parameters which must be considered in selectingthe predetermined comparison value, including the tonnage of the airconditioner, the air flow rate through the evaporator, and the locationof the thermistors in the airstream.

Returning to the present example (FIG. 4), if the temperature differenceacross A coil 52 is determined (symbol 74) to be less than or equal to12° F., or greater than or equal to 30° F., an incipient failure of theenvironmental control system is anticipated and indicated by theinventive apparatus. Thus, branching rightward from symbol 74, it can beseen that the indicator apparatus alarm is initialized or activated, inwhich case LED 34 will flash, and an audible signal such as a buzzerwill emanate from speaker 36 if switch 38 is closed. As shown in buzzerbranch 76 of the logic flowing from symbol 78, the buzzer may bedisabled by opening switch 38. Although the buzzer may be disabled, LED34 will continue to flash until the thermostat mode is changed to “off”or “heating”, or until the problem with the environmental control systemhas been corrected to bring the sensed temperature difference across Acoil 52 into its proper operating range, above 12° F. and below 30° F.Note that although the alarm may be activated (symbol 78), theenvironmental control system has not yet completely failed. Thus theoccupants may still be provided with some level of comfort whileawaiting repairs, or the warned occupant may alternatively choose toturn off the environmental control system at the thermostat, therebypossibly averting damage to the system.

Returning now to symbol 70, if cooling is not called for according tothe thermostat signal, the logic branches to the right, to symbol 80,and the inquiry is made as to whether heating is called for. If heatingis not called for, the logic will branch upward from symbol 80 to theinput of symbol 66, and the logic will enter a new cycle. If heating iscalled for, the logic branch follows a rightward path from symbol 80 tosymbol 82, wherein a comparison of thermostats 62 (T₁) and 64 (T₂) ismade. Here, where heating is called for, it will be understood thatdownstream thermistor 64 should be at a higher temperature than upstreamthermistor 62, and so rather than taking a difference between T₁ and T₂,as shown in symbol 74, the difference between T₂ and T₁ is taken. Thisdifference is compared with a predetermined value of 7° F. As discussedabove regarding predetermined values 12° F. and 30° F., it is envisionedthat predetermined values slightly smaller and/or larger than 7° F. mayprovide adequate performance for assessing heating performance. Asmentioned above, the sensitivity or stability of the indicator apparatusmay be compromised by choosing alternative predetermined values,however.

If the sensed temperature difference across A coil 52 is greater than 7°F., no incipient failure of the environmental control unit is detectedand if the logic path returns to the input of symbol 72. If the sensedtemperature difference across A coil 52 is less than or equal to 7° F.,however, the logic branches downward from symbol 82 to activate thealarm (symbol 78) as described above with respect to a detectedincipient failure of the cooling system. As noted above, those skilledin the art will recognize that a similar control logic may beimplemented which will actuate an alarm should a sensed temperaturedifference across the heat exchanger be significantly greater than apredetermined value, which may be indicative of degraded airflowperformance.

As mentioned above, in the event of the alarm (symbol 78) beingactivated, the occupants would then contact the appropriate repairfacility to have the matter investigated and corrected. Alternatively,the inventive incipient failure indicator apparatus may be provided withan optional notification system which, upon activation of the alarm(symbol 78), would activate another, remote alarm system (symbol 84,FIG. 4), which may be dedicated to environmental control systemmonitoring via a telephone line, for example, or which may be tied intoa preexisting building alarm system, to provide notification of theincipient environmental control system failure to persons locatedoutside of the building served by the environmental control system. Adedicated remote alarm system may provide instant notification to anappropriate repair facility that an incipient failure of theenvironmental control system has been detected, and the repair personnelmay then quickly respond to the alarm, providing shorter time to repaira failed system or correcting the problem from complete failure occurs.

Referring now to FIG. 5, there is shown an alternative environmentalcontrol system unit to which the inventive incipient failure indicatingapparatus is adapted. Rather than being a heat pump system,environmental control unit 46 a is a combination furnace and airconditioner unit of the type well known in the art, which, like heatpump unit 46 (FIG. 3), comprises filter 58, blower 50 and A coil 52 a,which serves solely as the evaporator for an air conditioner refrigerantsystem (not shown), disposed within housing 48 a. Additionally, unit 46a includes heat exchanger (or heater core) 86 by which the furnacetransfers heat to the air flowing through housing 48 a. As is usual, hotcombustion gases from a burner flow through the interior passages ofheater core 86.

Under the influence of blower 50, air flows upward within housing 48 a,as indicated by arrows 60, through filter 58, blower 50 itself, heatercore 86 and A coil 52 a to ductwork 54. Thermistors 62 and 64 arerespectively placed upstream and downstream of both heater core 86 and Acoil 52 a, thereby measuring the temperature difference across both heatexchangers, only one of which is operation at a given time, depending onwhether heating or cooling is being called for by the thermostat. Thus,in combination unit 46 a, thermistors 62 and 64 may, as in the case ofheat pump unit 46, be used to determine the assessed difference in boththe heating and cooling modes. The logic associated with detecting anincipient failure of environmental control unit 46 a is essentiallyidentical to that shown in FIG. 4, with the exception that no auxiliaryheater signal will be received or included in any logical determination.

Referring now to FIG. 6, there is shown a second embodiment of acombination air conditioning and furnace environmental control unit towhich the inventive incipient failure indicator apparatus is adapted.Environmental control unit 46 b is identical to environmental controlunit 46 a (FIG. 5) with the exception that instead of providing only twothermistors, 62, 64, respectively disposed upstream and downstream ofboth heat exchanger 86 and A coil 52 a, the incipient failure indicatorapparatus adapted to unit 46 b includes three thermistors. Thermistors62 and 64 are respectively disposed in the air stream upstream anddownstream of heater core 86. Thermistor 64 is also disposed upstream ofA coil 52 a, while third thermistor 88 is disposed downstream of A coil52 a. With reference again to FIG. 4, thermistor 88 provides a thirdthermistor input T₃ to the control logic of indicator unit 26, as shownin ghosted lines. According to this alternative embodiment, symbol 74 ofthe flowchart is replaced with symbol 74 a, shown in ghosted line. Thus,when cooling is called for, the difference between temperatures sensedby thermistors 64 (T₂) and 88 (T₃) will be compared with thepredetermined values of 12° F. and 30° F., the remainder of the logicassociated with FIG. 4 otherwise unchanged. Those skilled in the artwill now understand that A coil 52 a may be provided with a dedicatedpair of thermistors upstream and downstream thereof, with thermistors 62and 64 dedicated to determining the temperature difference across heatexchanger 86 alone.

Returning again to the flow chart of FIG. 4 (symbol 66), if a thermostator auxiliary heating signal is recognized, the logic also proceedsrightward along filter maintenance branch 90. The logic flows alongbranch 90 through reset time switch 42, and a timer provided in thecontrol board of indicator unit 26 assesses the accumulated blower runtime. If the accumulated blower running time is greater than 480 hours,the logic continues rightward from symbol 92 to illuminate LED 40. Ifthe blower running time is less than or equal to 480 hours, the logicloops back to the input to symbol 92, whereby the timer continues to runduring times the blower signal is received by indicator unit 26. Thusthe counter associated with symbol 92 accumulates only that time inwhich blower 50 (FIGS. 3, 5 and 6) is actually in operation, which has adirect bearing on filter life. Once the filter has been cleaned orreplaced, the occupant will press reset time switch 42, which will resetthe timer associated with symbol 92. Alternatively, this aspect of thepresent invention may be simplified somewhat by illuminating lamp 40every 480 hours following reset of switch 42 regardless of whether ablower signal is received. According to such an embodiment, wherein lamp40 will illuminate after a period of time regardless of how much blower50 has operated during that period, the illumination of lamp 40 is to beregarded as a reminder to the occupant to check the condition of filter58, and to replace it as required. The filter timer would be reset toilluminate lamp 40 after another 480 hours have passed by depressingswitch 42. Another alternative embodiment would base the filter servicetime period on accumulated compressor running time, rather than onaccumulated blower running time. Compressor operation is closely relatedto blower operation, especially if the environmental control unit is aheat pump or during air conditioner operation of a combinationenvironmental control unit. In some applications, an indication that thecompressor is being powered may be more readily obtained than anindication that the blower is being powered. Further, the logic of theinventive incipient failure indicator apparatus may also be adapted toflash lamp 40 in the event of a sensor failure, alerting the occupant tothe need for an appropriate repair.

While this invention has been described as having exemplary designs, thepresent invention can be further modified within the spirit and scope ofthis disclosure. This application is therefore intended to cover anyvariations, uses, or adaptations of the invention using its generalprinciples. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains and which fallwithin the limits of the appended claims.

What is claimed is:
 1. An incipient failure indication apparatus for anenvironmental control system, said system controlling the temperature ofthe air in a living space, said system including a heat exchangerthrough which air flows and a temperature control thermostat, saidthermostat located in said living space, said apparatus comprising: anindicator mounted substantially adjacent to the thermostat, saidindicator including an alarm and a control board, said alarm incommunication with said control board, said control board incommunication with the said thermostat, said alarm comprising one of avisual indicator and an aural indicator for attracting the attention ofa person in said living space to said indicator upon activation of saidalarm; a first temperature sensor disposed on the upstream side of thesaid heat exchanger, a second temperature sensor disposed on thedownstream side of the said heat exchanger, said temperature sensorsrespectively sensing the temperature of the air on the upstream anddownstream sides of the heat exchanger, said first and secondtemperature sensors in communication with said control board, saidcontrol board having a comparator which compares the temperatures sensedby said first and second temperature sensors, and an activator foractivating said alarm in response to a determination by said comparatorof a difference in temperatures sensed by said first and secondtemperature sensors which is one of less than and greater than apredetermined value.
 2. An incipient failure indication apparatusaccording to claim 1, wherein said indicator and the thermostat haveseparate housings.
 3. An incipient failure indication apparatusaccording to claim 1, wherein said indicator and the thermostat areprovided in a common housing.
 4. An incipient failure indicationapparatus according to claim 1, wherein said alarm includes both avisual indicator and an aural indicator, said apparatus furthercomprising a switch intermediate and connected to said control board andsaid aural indicator, whereby communication between said control boardand said aural indicator may be selectively interrupted.
 5. An incipientfailure indication apparatus according to claim 1, wherein saidindicator further comprises means for initiating a timer upon receivinga signal from the thermostat, wherein said means for comparing thetemperatures sensed by said first and second temperature sensors isactivated only after a predetermined period measured by said timer. 6.An incipient failure indication apparatus of claim 1 for anenvironmental control system which includes a heat exchanger throughwhich air flows, a temperature control thermostat, and a replaceable airfilter in fluid communication with the heat exchanger for cleaning theair which flows through the heat exchanger, wherein said apparatusincludes a timer, and said indicator including a filter service timeindicator and a reset switch in communication with said timer, saidapparatus including means for activating said filter service timeindicator a predetermined period after activation of said reset switch.7. An incipient failure indication apparatus according to claim 6,wherein said reset switch is a pushbutton switch.
 8. An incipientfailure indication apparatus according to claim 6, wherein said filterservice time indicator is a light.
 9. An incipient failure indicationapparatus according to claim 8, wherein said alarm is a visualindicator, said visual indicator a light, said filter service timeindicator light and said alarm indicator light having perceptivelydifferent colors.
 10. An incipient failure indication apparatus for anenvironmental control system, said system controlling the temperature ofthe air in a living space, said system including a heat exchangerthrough which air flows and a temperature control thermostat capable ofcalling for heating and cooling of said living space, said thermostatlocated in said living space, said apparatus comprising: an indicatormounted substantially adjacent to the thermostat, said indicatorincluding an alarm and a control board, said alarm in communication withsaid control board, said control board in communication with the saidthermostat, said alarm comprising one of a visual indicator and an auralindicator for attracting the attention of a person in said living spaceto said indicator upon activation of said alarm; a first temperaturesensor disposed on the upstream side of the said heat exchanger, asecond temperature sensor disposed on the downstream side of the saidheat exchanger, said temperature sensors respectively sensing thetemperature of the air on the upstream and downstream sides of the heatexchanger, said first and second temperature sensors in communicationwith said control board, said control board having a comparator whichcompares the temperatures sensed by said first and second temperaturesensors, and an activator for activating said alarm in response to adetermination by said comparator of a difference in temperatures sensedby said first and second temperature sensors which is one of less thanand greater than a predetermined value; means for recognizing which ofheating and cooling is called for by the said thermostat and means forcomparing a sensed temperature difference between said first and secondtemperature sensors to a first said predetermined value if heating iscalled for and to a second said predetermined value if cooling is calledfor; and means for detecting the application of auxiliary heating and,and in response to such detection, deferring the comparison of thetemperatures sensed by said first and second temperature sensors whenauxiliary heating is detected until no auxiliary heating is detected.11. An incipient failure indication apparatus according to claim 10,wherein said first predetermined value is approximately 7° F.
 12. Anincipient failure indication apparatus according to claim 10, whereinsaid second predetermined value is approximately 12° F.
 13. An incipientfailure indication apparatus for an environmental control system forcontrolling the temperature of the air in a living space, said systemincluding first and second heat exchangers through which air flows inseries and a temperature control thermostat, said thermostat located insaid living space, said apparatus comprising: an indicator mountedsubstantially adjacent to the thermostat, said indicator including analarm and a control board, said alarm in communication with said controlboard, said control board in communication with the said thermostat,said alarm comprising one of a visual indicator and an aural indicator,for attracting the attention of a person in said living space to saidindicator upon activation of said alarm; a first temperature sensordisposed on the upstream side of the said first heat exchanger, a secondtemperature sensor disposed on the downstream side of the said secondheat exchanger, said temperature sensors respectively sensing thetemperature of the air on the upstream and downstream sides of the heatexchangers, said first and second temperature sensors in communicationwith said control board, said control board having a comparator whichcompares the temperatures sensed by said first and second temperaturesensors, and an activator for activating said alarm in response to adetermination by said comparator of a difference in temperatures sensedby said first and second temperature sensors which is one of less thanand greater than a predetermined value.
 14. An incipient failureindication apparatus for an environmental control system which includesfirst and second heat exchangers through which air flows in series and atemperature control thermostat, as claimed in claim 13, furthercomprising a third temperature sensor disposed intermediate the firstand second heat exchangers, whereby said first and third temperaturesensors respectively sense the temperature of the air upstream anddownstream of the first heat exchanger and said third and secondtemperature sensors respectively sense the temperature of the airupstream and downstream of the second heat exchanger, said thirdtemperature sensor in communication with said control board.
 15. Anincipient failure indication apparatus according to claim 14, whereinsaid apparatus further comprises means for recognizing which of heatingand cooling is called for by the thermostat and means for comparing atemperature difference sensed between each of a first pair oftemperature sensors, said first pair including said first and thirdtemperature sensors, and comparing a temperature difference sensedbetween each of a second pair of temperature sensors, said second pairincluding said third and second temperature sensors, and means foractivating said alarm in response to recognizing one of a difference intemperature sensed by said first pair which is greater than a firstpredetermined value and a difference in temperature sensed by saidsecond pair which is greater than a second predetermined value.
 16. Anincipient failure indication apparatus according to claim 15, whereinsaid apparatus further comprises means for detecting the application ofauxiliary heating and deferring the comparison of the temperaturessensed by one of said first and second pairs when auxiliary heating isdetected until no auxiliary heating is detected.
 17. An incipientfailure indication apparatus according to claim 14, wherein one of saidfirst and second predetermined values is approximately 7° F.
 18. Anincipient failure indication apparatus according to claim 17, whereinsaid means for recognizing which of heating and cooling is called for bythe thermostat recognizes that heating is called for and compares asensed difference in air temperature between the two temperature sensorsof one said pair with said approximately 7° F. predetermined value. 19.An incipient failure indication apparatus according to claim 14, whereinone of said first and second predetermined values is approximately 12°F.
 20. An incipient failure indication apparatus according to claim 19,wherein said means for recognizing which of heating and cooling iscalled for by the thermostat recognizes that cooling is called for andcompares a sensed difference in air temperature between the twotemperature sensors of one said pair with said approximately 12° F.predetermined value.